This study may determine whether laboratory studies of people's blood cells, who have received vaccines against H5 influenza, or "bird flu," will help to decide if the vaccines are going to be prevent disease effectively. About 232 people, 18 years and older, enrolled in the studies "A Randomized, Double-Blinded, Placebo-Controlled, Phase I/II, Dose-Ranging Study of the Safety, Reactogenicity, and Immunogenicity of Intramuscular Inactivated Influenza A/H5N1 Vaccine in Healthy Adults" and "in Healthy Elderly Adults" will participate. Participants may be involved in this study for about 14 months. Procedures may include blood draws, physical exams, and medical history reviews.